NationStates Jolt Archive

So we have had a Numbers Enigma and a Probability Puzzle. Now for a Mechanics Mystery.


A plane is standing on runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane wheel speed and tunes the speed of the conveyer to be exactly the same, but in the opposite direction.
Will the plane be able to accelerate down the runway and take off?

Clarification:
The wheels and conveyor belt will not suffer from friction in the bearings or mechanical failure. The wheels DO have friction with the runway in the same way your car wheels have friction on the road.

No. Planes take off by the lift on the wings, caused by the speed of the air passing over them. If the plane isn't actually moving, then this would not happen, not matter how quickly the wheels were turning.

x m/s west + x m/s east = a total vector of 0 m/s standing still

west

however relatively to the conveyerbelt the plane will be moving at 2x m/s

We're talking about plain vanilla fixed-wing aircraft, right? No ornithopters, heliplanes, etc?

Remember - planes do not get thrust from the wheels, they get thrust from the engines.

Look at the forces on the plane and think about how plane wheels work.

We're talking about plain vanilla fixed-wing aircraft, right? No ornithopters, heliplanes, etc?

Normal fixed wing plane.

Nothing funky.

For simplicity assume it's a 737.

Remember - planes do not get thrust from the wheels, they get thrust from the engines.

Look at the forces on the plane and think about how plane wheels work.

Bah, I change my vote.... wheels are only there to help steer it.

As the engine starts pushing the plane forward the wheels start to turn the conveyer starts turning to pushing the wheels twice as fast as they would be. But as the thrust as FR so eloquenlty put it is from the engines the only effect that the conveyerbelt has is to make the wheels spin twice as fast as the speed of the plane.

I knew there was a catch in there somewhere... Please change vote to take off.

I knew there was a catch in there somewhere... Please change vote to take off.

But no matter the 'speed' of the plane, it still isn't actually moving. If it's not moving, then the required pressures never form on the wings, and it will never take off.

But no matter the 'speed' of the plane, it still isn't actually moving. If it's not moving, then the required pressures never form on the wings, and it will never take off.

Yeah, but all the conveybelt is doing is spinning the wheels two times faster than they would normally be. As the spinning of the wheels does not change the amount of force exerted by the engines in propelling the plane forward then the plane is moving forward. The wheels are only there to reduce friction on the tarmac(on this case the conveyerbelt) as much as possible

So we have had a Numbers Enigma and a Probability Puzzle. Now for a Mechanics Mystery.


A plane is standing on runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane wheel speed and tunes the speed of the conveyer to be exactly the same, but in the opposite direction.
Will the plane be able to accelerate down the runway and take off?

Clarification:
The wheels and conveyor belt will not suffer from friction or mechanical failure.

Although I assume there is friction between the wheels and conveyor belt but they wont be damaged by it?

What I mean is that if there isnt friction between the two would the plane not just slide along the ground

Yeah, but all the conveybelt is doing is spinning the wheels two times faster than they would normally be. As the spinning of the wheels does not change the amount of force exerted by the engines in propelling the plane forward then the plane is moving forward. The wheels are only there to reduce friction on the tarmac(on this case the conveyerbelt) as much as possible

I don't get it.

But I'll trust you.

Although I assume there is friction between the wheels and conveyor belt but they wont be damaged by it?

What I mean is that if there isnt friction between the two would the plane not just slide along the ground

I meant the bearings in the wheels and the mechanics of the conveyor belt do not suffer from friction/heating/breakdown.

The wheels experience friction in relation to the belt as normal.

Bah, I change my vote.... wheels are only there to help steer it.

As the engine starts pushing the plane forward the wheels start to turn the conveyer starts turning to pushing the wheels twice as fast as they would be. But as the thrust as FR so eloquenlty put it is from the engines the only effect that the conveyerbelt has is to make the wheels spin twice as fast as the speed of the plane.

I knew there was a catch in there somewhere... Please change vote to take off.

Not sure how to do that... Will remember the answers are one out.:)

Congrats on the quick pick up of the problem. I know people with First Class math degrees who take a looooong time to get this one

I don't get it.

But I'll trust you.

Okay, imagine this...

You have a wheel and are holding it by a bar that comes from the centre of the wheel. You push the wheel down and along the same conveyerbelt

What happens... The wheel turns twice as fast but as your hands (like the engines) are pushing the wheel forward the wheel still moves forward it just spins faster.

Okay, imagine this...

You have a wheel and are holding it by a bar that comes from the centre of the wheel. You push the wheel down and along the same conveyerbelt

What happens... The wheel turns twice as fast but as your hands (like the engines) are pushing the wheel forward the wheel still moves forward it just spins faster.

Ah, I see, I can understand that. But, I still don't see why the plane would take off. Even if the plane is still moving forwards, it is doing so on the spot (if it wasn't, it would come off the front of the belt).

If it is staying on the spot, then no matter how quickly it is moving 'forwards', there is no air pressure on the wings, and so there is no lift created. In other words, the plane could go really, really quickly in a forward direction, but it would stay on the ground.

Even if the thrust is coming from the engines, the wheels allow the plane to move on the ground. The plane could only take off if the wheels broke off.

Mind you, this is coming from someone with no knowledge of physics.

Ah, I see, I can understand that. But, I still don't see why the plane would take off. Even if the plane is still moving forwards, it is doing so on the spot (if it wasn't, it would come off the front of the belt).

If it is staying on the spot, then no matter how quickly it is moving 'forwards', there is no air pressure on the wings, and so there is no lift created. In other words, the plane could go really, really quickly in a forward direction, but it would stay on the ground.

When the engines start, the plane moves forward at the usual speed relative to the ground (and more importantly the air), regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is to make the plane's wheels spin madly.

I don't get it.

But I'll trust you.

Imagine you have a toy car on a conveyor.

The conveyor moves opposite to the direction you are pushing.

Is it possible for you to push the car forwards?

Hopefulyl you say yes.


What happens the wheels are basically freely spinning, while the plane moves forward. The only difference is the wheels are spinning twice as fast as they would be if the conveyor was still.

If you were driving a car then it would stay still - as the speed of the car is dependant on the speed of the wheels as it gets powered through the wheels. The plane is powered through the propellor/jet - the wheels just help steer when on the ground and allow the plane to roll forwards rather than have the metal of the base of the plane slide against the runway during takeoff.


Imagine it with forces. The 'backwards' force throught he wheels is very small. To forwards force from the jet is very very very large. The backwards force through the wheel sumbtracts a tine ammount from the forwards force from the jet. There is a net forwards force and therefore the jet allelerates and takes off.

The conveyor is set to match the speed of the wheels. The faster the wheels spin the faster the conveyor spins, so the engines won't be able to propel the plane at all, and if the plane can't move then it can't take off.

Ah, I see, I can understand that. But, I still don't see why the plane would take off. Even if the plane is still moving forwards, it is doing so on the spot (if it wasn't, it would come off the front of the belt).

If it is staying on the spot, then no matter how quickly it is moving 'forwards', there is no air pressure on the wings, and so there is no lift created. In other words, the plane could go really, really quickly in a forward direction, but it would stay on the ground.

I think you are missing the point, the plane is not staying still, as like the example the wheel/plane does go forward because the force that makes the wheel/plane move (your hands/engine) is not effected by the conveyerbelt.

All the conveybelt does is change the speed of a free-wheeling wheel, from an observer point of view the plane is still moving at it's speed just one of the wheels it is on is going at 2 times that speed

The conveyor is set to match the speed of the wheels. The faster the wheels spin the faster the conveyor spins, so the engines won't be able to propel the plane at all, and if the plane can't move then it can't take off.

Remember - the plane is not powered by the wheels, it is powered by the jet/prop which moves reative to the wind.

I think you are missing the point,
Of this I have no doubt. :p

the plane is not staying still, as like the example the wheel/plane does go forward because the force that makes the wheel/plane move (your hands/engine) is not effected by the conveyerbelt.

All the conveybelt does is change the speed of a free-wheeling wheel, from an observer point of view the plane is still moving at it's speed just one of the wheels it is on is going at 2 times that speed

I sort of see what your getting at now. Even if the wheels were moving backwards, the force of the engines would still push the plane forwards (although you'd knacker your tires). Right?

Remember - the plane is not powered by the wheels, it is powered by the jet/prop which moves reative to the wind.

Well I figured to the plane to be able to move forward and take off it needs the wheels to spin at a certain speed relative to the ground, so that it can move through the air and the wings will generate lift. But in this case the ground is always moving in the opposite direction at the same speed. So if the plane isn't moving relative to the air around it, there won't be any lift and it'll stay put.

Well I figured to the plane to be able to move forward and take off it needs the wheels to spin at a certain speed relative to the ground, so that it can move through the air and the wings will generate lift. But in this case the ground is always moving in the opposite direction at the same speed. So if the plane isn't moving relative to the air around it, there won't be any lift and it'll stay put.

The thing is the engines move relative to the air.

The engines will push the plane forwards, but the wheels will freely spin backwards at twice the speed of the relative forwards motion.


Imagine you have the plane on a winch. The runway start moving against your motion. Is it possible to winch/drag the plane forward?

Meh, I'm crap at physics anyway.

So we have had a Numbers Enigma and a Probability Puzzle. Now for a Mechanics Mystery.


A plane is standing on runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane wheel speed and tunes the speed of the conveyer to be exactly the same, but in the opposite direction.
Will the plane be able to accelerate down the runway and take off?

Clarification:
The wheels and conveyor belt will not suffer from friction in the bearings or mechanical failure. The wheels DO have friction with the runway in the same way your car wheels have friction on the road.

Thats a nasty positive feed back loop there with the wheels and the conveyer belt.

The plane will take off becasue it is powered by the engines and lift under the wings is dependent on the plane relative to the air not the ground.

As the plane will move along no matter what the conveyer does the wheels will start spinning faster and faster as the conveyer speeds up to try and equal the speed of the wheels. That means the wheels should always be spinning twice as fast as the conveyer belt (though a lot lot faster than they would if there was not a conveyer belt).

Damn, I just realised I voted for the wrong option, I meant to click that it would take off.

Edit is in bold, correcting my mistake due to rapid typing.

Again, as in the other Monte Hall question, this was asked and answered in the Straight Dope by Cecil Adams.

http://www.straightdope.com/columns/060203.html

Again, as in the other Monte Hall question, this was asked and answered in the Straight Dope by Cecil Adams.

http://www.straightdope.com/columns/060203.html

This, I understood. :)

Maybe I should go back to last night's Monty Hall thread, read his take on that one, too, and hope for a miracle. :p

Update: Yeah, not so much with the miracles today... >.<

Thats a nasty positive feed back loop there with the wheels and the conveyer belt.

The plane will take off becasue it is powered by the engines and lift under the wings is dependent on the plane relative to the air not the ground.

As the plane will move along no matter what the conveyer does the wheels will start spinning faster and faster as the conveyer speeds up to try and equal the speed of the wheels. That means the wheels should always be spinning twice as fast as the conveyer belt (though a lot lot faster than they would if there was not a conveyer belt).

Damn, I just realised I voted for the wrong option, I meant to click that it would take off.

Edit is in bold, correcting my mistake due to rapid typing.

I don't get it.

The aircraft has no ground speed, that's true.

But it also has no airspeed, only the jet flux through the intake.

When no air flows over the wings, how can it take off?

I'm appalled by the number of people that chose "stay still". It should be zero.

I'm appalled by the number of people that chose "stay still". It should be zero.

Similarly the number of posts like this should be zero, but alas the world is rarely as it should be.

Similarly the number of posts like this should be zero, but alas the world is rarely as it should be.

LOL

It shouldn't take a physics degree (or any physics for that matter) to be able to figure this out. All it does take is the ability to think critically/analytically which anyone is capable of, they just have to try.

I get it now. The wheels just spin to the point they would suffer damage because the ball bearings in the wheels have no friction. While the plane sits there, it will move backwards with the conveyor, as the engine builds thrust, the wheels just become even more irrelevant contacts with the ground. The wheels do not move on their own and thus a dynamic conveyor speed cannot stop the plane from moving because unlike a car it's mobility comes from a source uneffectable by the conveyor belt. Like tieing a toy car so that it is always straight on a treadmill. The friction pulling back on the wheels from the treadmill can never exceed the strength of the string because the wheels spin freely.

LOL

It shouldn't take a physics degree (or any physics for that matter) to be able to figure this out. All it does take is the ability to think critically/analytically which anyone is capable of, they just have to try.

Again, the world is rarely as it should be.


Oh, and this problem clearly takes more than the ability to think critically and/or analytically, it requires some knowledge of how aeroplanes work.

Again, the world is rarely as it should be.


Oh, and this problem clearly takes more than the ability to think critically and/or analytically, it requires some knowledge of how aeroplanes work.

It is a bit harder than that even, as even people with a decent knowlege of these things have trouble with it due to the counter intuitive nature of the situation.

I secretly install a steam driven catapault on the conveyer belt, and make it so that the planes wheels don't even need to touch it, thus, it takes off easily.

It is a bit harder than that even, as even people with a decent knowlege of these things have trouble with it due to the counter intuitive nature of the situation.

There's that too.

...it requires some knowledge of how aeroplanes work.

Like what? That the locomotion doesn't come from the wheels? It's only difficult if you over analyze it. People with lots of college degrees and less real world experience seem to get caught up with this one more than others. I suspect atleast half of the "stay still" answers realized they jumped a conclusion too quickly right after pressing "vote now".

It's easy to get caught up in over examining it because the question purposely steers you to concentrate on the wrong component. If you step back and look at the whole picture, there isn't much to think about. But trust me, you don't need to know any details about trust, lift, fluid dynamics, etc. Only thing to know is how it gets forward motion.

Like what? That the locomotion doesn't come from the wheels? It's only difficult if you over analyze it.

It's easy to get caught up in over examining it because the question purposely steers you to concentrate on the wrong component. If you step back and look at the whole picture, there isn't much to think about. You don't need to know any details about trust, lift, fluid dynamics, etc. Only thing to know is how it gets forward motion.

No, like the plane's groundspeed is(apparently) irrelevant and that only it's airspeed matters.

Side question: as the speed of the conveyor depends on reacting to the speed of the craft's wheels, are the craft's wheels always moving somewhat faster than the conveyor belt when the craft accelerates?

Side question: as the speed of the conveyor depends on reacting to the speed of the craft's wheels, are the craft's wheels always moving somewhat faster than the conveyor belt when the craft accelerates?
What do you mean?

What do you mean?

Are action and reaction simultaneous?

Are action and reaction simultaneous?

Assume the conveyor instantly matches the speed of the plane.

Assume the conveyor instantly matches the speed of the plane.

1. The speed of the plane or the speed of the rotation of the wheels?

2. Ah, so we are dealing with a physics and mechanics question which doesn't map onto real world physics or mechanics in at least two different ways (frictionless bearings and instantaneous response)? Somewhat unfair.

Assume the conveyor instantly matches the speed of the plane.

Now that hurst my brain as the wheels rapidly go to infinity spinning speed. If there was a delay then it is not so much a problem. All this of course is irrelavent to the question.

Now that hurst my brain as the wheels rapidly go to infinity spinning speed. If there was a delay then it is not so much a problem. All this of course is irrelavent to the question.

How ould you get infinite speed from a finite force?

The wheels exceed stress limits and break off and the plane crashes to it's belly on the runway and explodes killing everyone aboard, but never taking off.

The wheels only support the weight of the plane while the wings do not carry it (yet), the movement is a result of the engines thrusting air behind the plane. Ergo it should be of no relevance what the wheels do or a conveyor beneath.

The wheels only support the weight of the plane while the wings do not carry it (yet), the movement is a result of the engines thrusting air behind the plane.

This is not always the case.

The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane wheel speed and tunes the speed of the conveyer to be exactly the same, but in the opposite direction.

So if the wheels move one metre upwards the conveyor moves one metre downwards?

This is not always the case.
In take-off it is. It's not the wheels that accelerate the plane.

Wait, wait. The engine is going? I didn't see anything about that.

In take-off it is. It's not the wheels that accelerate the plane.

Do the letters VTOL mean anything to you? - a Harrier jumpjet would be a good example here, where certainly it is movement of air which causes takeoff, but not in all cases movement behind the craft.

I'm not claiming that the wheels accelerate the plane to takeoff speed (although it may very well be that there is some strange kind of plane where this is the case). A case could also be made for a catapult launched glider being another exception.

I'm not just being pedantic here to be annoying, just examining the possibilities.

to take off the plane needs air moving at sufficient speed over it's wings to produce lift. if the conveyer is moving at the same speed as the wheels are turning the plane is not moving through the air only (sort of) over the ground, therefore it will not take off.

actually i think bazalonia might be right but i don't know anything about mechanics or maths or anything so i can't think it through. certainly sounds convincing.

Ah wait now i get it. It's not paradoxial or counter-intuitive, it's just an unclear question.

As has been said the movement of the air around the wings is what provides lift, not the movement of the wheels. With no forward motion the plane cannot achieve lift, thus no takeoff.

There's a reason ships hurl planes off of carriers rather than having them just sit on conveyors (which would take up much less space), it can't work.

How ould you get infinite speed from a finite force?

Ok the plane relative to the rest of the world will be moving along the conveyor belt picking up speed to take off. The conveyor belt moves in the oposite direction to the plane and always equals the speed of the wheels spinning.

Now as the speed of the conveyor belt will not affect or stop the plane from accelerating like normal this means it will move along the conveyor belt. As it does this the wheels will rotate faster than the conveyor belt is moving. The conveyor will speed up instantly to that speed of the wheels, but in doing so it makes the wheels spin even faster and so the conveyor instantly speeds up to match this speed. This is all occuring instantly so no time has passed and therefore the wheels and conveyor will instantly go infinite speed as soon as the plane starts moving.

If the plane moves 1m left the conveyor belt will initially try moving at a speed such that the plane if accelerated by the wheels would stay stationary, therefore move 1m right. Now the wheels will need to rotate at a speed to cover the 2m difference as that is the difference between the conveyor and rest of the plane. The conveyor is designed to match the speed of the wheels so it speeds up to moving 2m but that makes the wheels spin even faster. This then means the conveyor speeds up again but that speeds up the wheels, this keeps on happening untill the plane takes off. Now because the conveyor always matches the wheels speed and does this instantly you instantly get to a silly situation which is infinitly fast spinning wheels.

I repeated myself, oh well. I hope this helps.

The wheels exceed stress limits and break off and the plane crashes to it's belly on the runway and explodes killing everyone aboard, but never taking off.

This is the correct answer. "Stay still" was closer to it, so it got my vote.

It doesn't matter if the Jets are running, in any real world aircraft, forward movement is *Always* supplied by the main means of propulsion (either Jet thruster or Propeller) regardless of whether the aircraft is on the ground or not, in this case, no matter how fast the jets push the plane, the conveyor always equals imparted velocity so that net velocity of the aircraft is 0m/s.

Unless the wind is in excess of 50-150 m/s (we're talking cat 4-5 hurricane level winds here) the plane won't take off, because with the conveyor, the net velocity of the aircraft is always going to be zero no matter what, it would take an outside force (such as the wind) to provide any movement of air over the wings to create lift.

Another vote for The gear assembly exceeds stress limits, everybody dies and I'm an engineer & smarter than you.
good day.

Ok the plane relative to the rest of the world will be moving along the conveyor belt picking up speed to take off. The conveyor belt moves in the oposite direction to the plane and always equals the speed of the wheels spinning.

Now as the speed of the conveyor belt will not affect or stop the plane from accelerating like normal this means it will move along the conveyor belt. As it does this the wheels will rotate faster than the conveyor belt is moving. The conveyor will speed up instantly to that speed of the wheels, but in doing so it makes the wheels spin even faster and so the conveyor instantly speeds up to match this speed. This is all occuring instantly so no time has passed and therefore the wheels and conveyor will instantly go infinite speed as soon as the plane starts moving.

If the plane moves 1m left the conveyor belt will initially try moving at a speed such that the plane if accelerated by the wheels would stay stationary, therefore move 1m right. Now the wheels will need to rotate at a speed to cover the 2m difference as that is the difference between the conveyor and rest of the plane. The conveyor is designed to match the speed of the wheels so it speeds up to moving 2m but that makes the wheels spin even faster. This then means the conveyor speeds up again but that speeds up the wheels, this keeps on happening untill the plane takes off. Now because the conveyor always matches the wheels speed and does this instantly you instantly get to a silly situation which is infinitly fast spinning wheels.

I repeated myself, oh well. I hope this helps.

The plane+conveyor system will only accelerate as long as the aircraft has fuel, and will only accelerate to the to the top speed of the aircraft (about 300 m/s, maybe 400 tops).

so, no infinitely fast wheels here

A planes thrust is provided by propeller or thrust ... their wheel speed has jack shit to do with their ability to take off

I am surprised how many people answered stay still, depressing.

It doesn't matter if the Jets are running, in any real world aircraft, forward movement is *Always* supplied by the main means of propulsion (either Jet thruster or Propeller) regardless of whether the aircraft is on the ground or not, in this case, no matter how fast the jets push the plane, the conveyor always equals imparted velocity so that net velocity of the aircraft is 0m/s.

Unless the wind is in excess of 50-150 m/s (we're talking cat 4-5 hurricane level winds here) the plane won't take off, because with the conveyor, the net velocity of the aircraft is always going to be zero no matter what, it would take an outside force (such as the wind) to provide any movement of air over the wings to create lift.

Another vote for The gear assembly exceeds stress limits, everybody dies and I'm an engineer & smarter than you.
good day.

No the net velocity in respect to the CONVEYOR is zero ... but sense propulsion and lift are provided by reference to wind the only effect the conveyor will have is making the wheels spin faster

A planes thrust is provided by propeller or thrust ... their wheel speed has jack shit to do with their ability to take off

I am surprised how many people answered stay still, depressing.

Except that without any forward movement there's no air movement around the wings, thus no lift.

I'm depressed by the number of people who think it'd take off.

A planes thrust is provided by propeller or thrust ... their wheel speed has jack shit to do with their ability to take off

I am surprised how many people answered stay still, depressing.

the thrust is provided sure, but the plane still has to have air moving over the wings in order to take off, all the thrust does is provide velocity relative to the air so that air DOES move over the wings

*is still an engineer

Except that without any forward movement there's no air movement around the wings, thus no lift.

I'm depressed by the number of people who think it'd take off.

What is to stop the plane from moving forward?

The conveyor providing resistance?

the thrust is provided sure, but the plane still has to have air moving over the wings in order to take off, all the thrust does is provide velocity relative to the air so that air DOES move over the wings

*is still an engineer

The but as far as I can understand with the op the air speed is not changed in any way shape or form just its contact with the ground.

So the plane WILL have air moving over its wings as it accelerates

Unless you are proposing also changing air movement too

The conveyor providing resistance?

To what? a free turning wheel that has no internal friction or mechanical failure?

From the op
The wheels and conveyor belt will not suffer from friction in the bearings or mechanical failure

The but as far as I can understand with the op the air speed is not changed in any way shape or form just its contact with the ground.

So the plane WILL have air moving over its wings as it accelerates

Unless you are proposing also changing air movement too

Air speed is gained by moving forward, if the ground beneath you is constantly moving backward at the same rate you accelerate your net speed is 0. No forward motion, no lift.

No the net velocity in respect to the CONVEYOR is zero ... but sense propulsion and lift are provided by reference to wind the only effect the conveyor will have is making the wheels spin faster

Do you know what you mean by "net velocity in relation to the conveyor"? Cuz, the converyor is moving backwards, if the plane has zero net velocity with that, isn't the plane moving backwards as well?

Air speed is gained by moving forward, if the ground beneath you is constantly moving backward at the same rate you accelerate your net speed is 0. No forward motion, no lift.

No air speed is gained by movement relative to the AIR not the ground.

I am standing still and have a 20 mile an hour wind blowing into me ... are you going to honestly tell me there is no 20 mile an hour wind cause I am not moving relative to the ground?

Air speed is gained by moving forward, if the ground beneath you is constantly moving backward at the same rate you accelerate your net speed is 0. No forward motion, no lift.

What if a plane was flying and it flew over a huge conveyor belt moving backwards at the same speed?

No air speed is gained by movement relative to the AIR not the ground.

I am standing still and have a 20 mile an hour wind blowing into me ... are you going to honestly tell me there is no 20 mile an hour wind cause I am not moving relative to the ground?

Except wind is not involved here.

Do you know what you mean by "net velocity in relation to the conveyor"? Cuz, the converyor is moving backwards, if the plane has zero net velocity with that, isn't the plane moving backwards as well?

Sorry you are right if the conveyor is moving backwards at the same speed the plane is moving forwards then it has zero absolute velocity to an outside observer not the conveyor, I mis typed

Thats not what is happening here to a stationary observer the plane is accelerating

Except wind is not involved here.

I know but you made a statement that ground speed effects wind speed
With my example I showed ground speed has nothing to do with wind speed

It has to do with YOU movement in relation to the air not your movement in relation to the ground

I know but you made a statement that ground speed effects wind speed
With my example I showed ground speed has nothing to do with wind speed

It has to do with YOU movement in relation to the air not your movement in relation to the ground

I did what? Keep your screennames straight.

I did what? Keep your screennames straight.

Sorry again

What if a plane was flying and it flew over a huge conveyor belt moving backwards at the same speed?

No contact, no effect.

If your wheels are touching the ground when you apply power with the engines you will be forced forward, the conveyor counters this, apparently instantly with no lag time you will stay still, the more you push the engines trying to get thrust the more the belt moves backward.

No matter how hard you push the engines to move you forward you will be pushed backward by the belt. Unless your engines become powerful enough to reach escape velocity.

No contact, no effect.

If your wheels are touching the ground when you apply power with the engines you will be forced forward, the conveyor counters this, apparently instantly with no lag time you will stay still, the more you push the engines trying to get thrust the more the belt moves backward.

No matter how hard you push the engines to move you forward you will be pushed backward by the belt. Unless your engines become powerful enough to reach escape velocity.

The conveyor makes the wheels turn, no?

Ok I am going to try to break this down all these small statements are killing me

A) A planes lift is generated by wind moving over its wings surface, so movement in relation to the air is EVERYTHING.

B) The planes wheels provide no thrust they are free spinning usualy except in a braking solution.

And sense friction or performance of the wheels are NOT a problem in this scenario.

With this the plane accelerates independently of the conveyor as there is no energy acting on the conveyor

If this were a car or wheel propelled vehicle I would absolutely agree with you. In this case they have almost nothing to do with the problem

Ok I am going to try to break this down all these small statements are killing me

A) A planes lift is generated by wind moving over its wings surface, so movement in relation to the air is EVERYTHING.

B) The planes wheels provide no thrust they are free spinning usualy except in a braking solution.

And sense friction or performance of the wheels are NOT a problem in this scenario.

With this the plane accelerates independently of the conveyor as there is no energy acting on the conveyor

If this were a car or wheel propelled vehicle I would absolutely agree with you. In this case they have almost nothing to do with the problem

Oy, he doesn't think the plane is moving, because that's what the question conveys. He doesn't care about air speed because, not too unreasonably assumed, there isn't any as far as he's concerned

No contact, no effect.

If your wheels are touching the ground when you apply power with the engines you will be forced forward, the conveyor counters this, apparently instantly with no lag time you will stay still, the more you push the engines trying to get thrust the more the belt moves backward.

No matter how hard you push the engines to move you forward you will be pushed backward by the belt. Unless your engines become powerful enough to reach escape velocity.

If you were to fly in with a forward velocity of 200 Miles per hour and touched your wheels to the conveyor belt moving 200 MPH backwards what would it do to the plane other then make the wheels spin at 400 miles per hour

Your flight only matters on your forward speed of 200 MPH

The conveyor makes the wheels turn, no?

Actually the conveyor would be countering the wheel's movement. In actuality the stress on the landing gear of the plane would be absurd.

Actually the conveyor would be countering the wheel's movement. In actuality the stress on the landing gear of the plane would be absurd.

Which is not an issue in this hypothetical ... in real life yes

But then your problem would not be your ability to take off because of thrust but merely wheel failure.

Actually the conveyor would be countering the wheel's movement. In actuality the stress on the landing gear of the plane would be absurd.

See, there's the problem with the question. The question implies that the conveyor belt moves backwards fast enough to stop the plane from moving. Truthfully, it just moves backwards at the same speed as the plane, but applies the speed, this force, to the wheels instead of the plane. If a plane without wheels was skidding along at 100mph, and the belt moved back 100mph, then yeah, the plane basically wouldn't move.

Which is not an issue in this hypothetical ... in real life yes

But then your problem would not be your ability to take off because of thrust but merely wheel failure.

Short of a vertical take off and landing system the only outcome of the scenario is that the plane runs out of fuel eventually and rolls backward off the belt.

Short of a vertical take off and landing system the only outcome of the scenario is that the plane runs out of fuel eventually and rolls backward off the belt.

No ... sense the wheels have absolutely no effect on the actual speed of the plane nor does the ground air speed is the only key

And the plane would be gaining air speed

See, there's the problem with the question. The question implies that the conveyor belt moves backwards fast enough to stop the plane from moving. Truthfully, it just moves backwards at the same speed as the plane, but applies the speed, this force, to the wheels instead of the plane. If a plane without wheels was skidding along at 100mph, and the belt moved back 100mph, then yeah, the plane basically wouldn't move.

Problem is the wheels are attached to the plane, if their forward movement is arrested so is the rest of the attached aircraft.

Short of a vertical take off and landing system the only outcome of the scenario is that the plane runs out of fuel eventually and rolls backward off the belt.

Khadgar, how do planes stop?

Problem is the wheels are attached to the plane, if their forward movement is arrested so is the rest of the attached aircraft.

Their forwoard movement isn't arrested, they just spin.

No ... sense the wheels have absolutely no effect on the actual speed of the plane nor does the ground air speed is the only key

And the plane would be gaining air speed

Not if it's not moving, and until you can overcome the gravity holding you to a moving surface that counters forward thrust you're not moving. Like I said, short of the engines reaching escape velocity you will not move.

Problem is the wheels are attached to the plane, if their forward movement is arrested so is the rest of the attached aircraft.

No its not they are free spinning with no friction

No ... sense the wheels have absolutely no effect on the actual speed of the plane nor does the ground air speed is the only key

And the plane would be gaining air speed

Ground air?

Khadgar, how do planes stop?

Depends on the plane.

Not if it's not moving, and until you can overcome the gravity holding you to a moving surface that counters forward thrust you're not moving. Like I said, short of the engines reaching escape velocity you will not move.

Who cares what speed the surface is moving? what does that have to do with the lift of the plane?

You keep thinking this is a car

Ground air?

Sorry there should have been a coma in there

Depends on the plane.

Give me some examples.

No its not they are free spinning with no friction

Well that's just silly, without friction they wouldn't even stick to the ground and the plane would be hurled off the belt because there'd be no friction to hold it to the ground, only gravity.

This question is unacceptably vague on important points.

Well that's just silly, without friction they wouldn't even stick to the ground and the plane would be hurled off the belt because there'd be no friction to hold it to the ground, only gravity.

This question is unacceptably vague on important points.

No friction inside the wheels. Read the OP kthxbai.


And yes, the question is a poor quality question, and not a paradox like the Monty Hall problem.

Well that's just silly, without friction they wouldn't even stick to the ground and the plane would be hurled off the belt because there'd be no friction to hold it to the ground, only gravity.

This question is unacceptably vague on important points.

There is friction between the ground and the wheel but no internal bearing friction which is all that matters to the plane in this case

The ground does not slow down the plane and sense the thrust and lift are provided by air the conveyor belt is absolutely irrelevant the only thing it would do is make the wheels spin faster which is not an issue here

Here this explains pretty well

http://www.newton.dep.anl.gov/askasci/phy05/phy05023.htm

Give me some examples.

Well planes on an aircraft carrier for instance use a hook to grab a big ol' arresting cable which drags them to a dead stop almost immediately. A commercial aircraft I believe relies on slowing their airspeed as much as possible and then applying a thrust reverser on each engine, countering the forward movement once they land.

Here this explains pretty well

http://www.newton.dep.anl.gov/askasci/phy05/phy05023.htm

Did you read that page? They're not in consensus as to what would happen, infact it looks very much like this thread.

Did you read that page? They're not in consensus as to what would happen, infact it looks very much like this thread.

Yes with a lot of the ones on there have good explanations of why it will actually take off.

No the net velocity in respect to the CONVEYOR is zero ... but sense propulsion and lift are provided by reference to wind the only effect the conveyor will have is making the wheels spin faster

Ohkhay, lets do a break down of forces acting on an aircraft (in this case we don't have to worry about strange case aircraft which I will get into later, because the aircraft in questiion was clarified to be a 737)
anyway here we go:

the jets provide thrust
Thrust results in acceleration
acceleration supplies velocity (non zero velocity is an effect of acceleration)
velocity provides air-speed
air-speed provides lift

without a non-zero net velocity, the airplane cannot fly.
Because the airplane is sitting on a conveyor that is always moving in direct opposition to the aircraft, its net movement with regards to the air is zero, it doesn't matter in this case where the thrust is coming from, the fact is that whatever thrust is being applied is only providing net velocity with regards to the conveyor, not with regards to the air. Without air-speed there is no lift.

Now, there are some aircraft (many small prop aircraft, also jet fighters with thrust-mass ratios greater than one, I.E. the F-16 and F-15) that can provide enough air-speed via prop-wash over the wings to cause lift (or in the case of the F-16/F-15, enough raw thrust to conquer gravity). one of those aircraft in this instance would be able to take off. Sadly, the 737 specified is not an aircraft that can provide enough thrust or air-speed irrespective of velocity to achieve sufficient lift for flight.

Yes with a lot of the ones on there have good explanations of why it will actually take off.

Lots of good explanations as to why it wouldn't either.

Ohkhay, lets do a break down of forces acting on an aircraft (in this case we don't have to worry about strange case aircraft which I will get into later, because the aircraft in questiion was clarified to be a 737)
anyway here we go:

the jets provide thrust
Thrust results in acceleration
acceleration supplies velocity (non zero velocity is an effect of acceleration)
velocity provides air-speed
air-speed provides lift

without a non-zero net velocity, the airplane cannot fly.
Because the airplane is sitting on a conveyor that is always moving in direct opposition to the aircraft, its net movement with regards to the air is zero
snip
No its not its net velocity is the velocity provided by the engines

As friction is not an issue in this hypothetical whatever the hell its wheels do is not a problem

Think of it this way

You are moving on a go kart and hold a toy car out against the ground

The wheels are spinning really fast right? now move your arm forward

As you would see it does not matter how fast the ground is moving backwards the car still acheves a forward velocity

How would the conveyor be any different? the wheels are completely free wheeling in this case so it dont matter how fast they spin

Lots of good explanations as to why it wouldn't either.

Are we reading the same link? I only saw one of the comments had an explanation as to why it wouldn't (second comment to the original proposition)

Ohkhay, lets do a break down of forces acting on an aircraft (in this case we don't have to worry about strange case aircraft which I will get into later, because the aircraft in questiion was clarified to be a 737)
anyway here we go:

the jets provide thrust
Thrust results in acceleration
acceleration supplies velocity (non zero velocity is an effect of acceleration)
velocity provides air-speed
air-speed provides lift

without a non-zero net velocity, the airplane cannot fly.
Because the airplane is sitting on a conveyor that is always moving in direct opposition to the aircraft, its net movement with regards to the air is zero, it doesn't matter in this case where the thrust is coming from, the fact is that whatever thrust is being applied is only providing net velocity with regards to the conveyor, not with regards to the air. Without air-speed there is no lift.

Now, there are some aircraft (many small prop aircraft, also jet fighters with thrust-mass ratios greater than one, I.E. the F-16 and F-15) that can provide enough air-speed via prop-wash over the wings to cause lift (or in the case of the F-16/F-15, enough raw thrust to conquer gravity). one of those aircraft in this instance would be able to take off. Sadly, the 737 specified is not an aircraft that can provide enough thrust or air-speed irrespective of velocity to achieve sufficient lift for flight.But the thrust produced by the engines pushes against the air, not the ground. It is the movement of the plane that generates the low pressure above the specially formed wings that would actually carry the plane. The thrust of the engines is only needed to put the plane in motion, not to carry it. The wheels or the ground have nothing at all to do with the plane taking off, otherwise there would be no water planes.

Sadly, the 737 specified is not an aircraft that can provide enough thrust or air-speed irrespective of velocity to achieve sufficient lift for flight.But 737s actually fly and only occasionally fall out of the sky, so they seem to be capable of generating enough velocity...

Ohkhay, lets do a break down of forces acting on an aircraft (in this case we don't have to worry about strange case aircraft which I will get into later, because the aircraft in questiion was clarified to be a 737)
anyway here we go:

the jets provide thrust
Thrust results in acceleration
acceleration supplies velocity (non zero velocity is an effect of acceleration)
velocity provides air-speed
air-speed provides lift

without a non-zero net velocity, the airplane cannot fly.
Because the airplane is sitting on a conveyor that is always moving in direct opposition to the aircraft, its net movement with regards to the air is zero, it doesn't matter in this case where the thrust is coming from, the fact is that whatever thrust is being applied is only providing net velocity with regards to the conveyor, not with regards to the air. Without air-speed there is no lift.

Now, there are some aircraft (many small prop aircraft, also jet fighters with thrust-mass ratios greater than one, I.E. the F-16 and F-15) that can provide enough air-speed via prop-wash over the wings to cause lift (or in the case of the F-16/F-15, enough raw thrust to conquer gravity). one of those aircraft in this instance would be able to take off. Sadly, the 737 specified is not an aircraft that can provide enough thrust or air-speed irrespective of velocity to achieve sufficient lift for flight.
Let's say for the sake of argument, that the jet engines provide 10000 lbf of force along the longitudinal axis of the aircraft. What force is resisting that? The plane will move as long as there is a net positive force. I don't care what the wheels or the conveyor belt does. The airplane has to move if the sum of all forces and moments acting on it are not zero.

Practically? Wheels break off as the conveyer belt accelerates to improbable speed as the plane starts to accelerate forward under force of engines. Plane then goes up a little bit and then lands hard, conveyer belt slings it for a mile long skid backwards.

Uuuugggly.

Practically? Wheels break off as the conveyer belt accelerates to improbable speed as the plane starts to accelerate forward under force of engines. Plane then goes up a little bit and then lands hard, conveyer belt slings it for a mile long skid backwards.

Uuuugggly.
But wait, once the wheels break off, they probably stop spinning, then the conveyor would stop.

Practically? Wheels break off as the conveyer belt accelerates to improbable speed as the plane starts to accelerate forward under force of engines. Plane then goes up a little bit and then lands hard, conveyer belt slings it for a mile long skid backwards.

Uuuugggly.

Absolutly in the real world ... though not in the hypothetical

Let's say for the sake of argument, that the jet engines provide 10000 lbf of force along the longitudinal axis of the aircraft. What force is resisting that? The plane will move as long as there is a net positive force. I don't care what the wheels or the conveyor belt does. The airplane has to move if the sum of all forces and moments acting on it are not zero.
Simple ... nice

Absolutly in the real world ... though not in the hypothetical

I imagine he's well aware of that.

Simple ... nice

How would that convince him that the conveyor belt isn't balancing it with 10000 lbf?

How would that convince him that the conveyor belt isn't balancing it with 10000 lbf?

Because as stated in the original post the wheels are free spinning and no internal friction

The contact with the ground provides no backwards force.

Oranges. My final answer.

Because as stated in the original post the wheels are free spinning and no internal friction

The contact with the ground provides no backwards force.

Ja, ja, prove that to him. That's what Myrmi's post fails to do.

How would that convince him that the conveyor belt isn't balancing it with 10000 lbf?

I guess I would need to hear what part of the friction in a rolling wheel, plus the friction between a rolling wheel and the conveyor belt, could provide that sort of force.

Since we've invented this imaginary treadmill, let's idealize the bearings in the wheels so that they won't seize, catch on fire, and burn the plane up.

We'll also idealize the tires so that they can run at higher than normal speeds without shredding.

Absolutly in the real world ... though not in the hypothetical

But with the wheels and the runway both moving so fast, how would it be possible for the pilot to maintain control of the plane long enough for there to be enough acceleration to provide lift? That's why I still maintain my "crash" answer, even given this hypothesis.

But wait, once the wheels break off, they probably stop spinning, then the conveyor would stop.Why should the wheels break off? As a matter of fact I do not really understand what the conveyor is supposed to do. Unlike a car the propulsion of a plane does not depend on ground contact. Once the engines are running the plane starts moving into one direction. The wheels then only spin (passively) because the plane is moving forward. A conveyor could then just counter the movement of the plane so the wheels don't spin at all while the plane gets faster. The conveyor would have to run in the same direction the plane is moving. If the conveyor was running in the opposite direction the spinning of the wheels would just double, but that would not alter the plane's movement.
Where is the solution now?

But wait, once the wheels break off, they probably stop spinning, then the conveyor would stop.
If the conveyor stops that suddenly, the belt will be heated enough to melt the bottom of the plane, I suspect. Think about how fast it'll be going before the wheels snap, and then how much kinetic energy is going to get dumped into thermal energy in braking.

If the conveyor stops that suddenly, the belt will be heated enough to melt the bottom of the plane, I suspect. Think about how fast it'll be going before the wheels snap, and then how much kinetic energy is going to get dumped into thermal energy in braking.

Hmm true...Then it's welded to whatever's left of the conveyor?

Hmm true...Then it's welded to whatever's left of the conveyor?
And probably on fire, if you're not lucky.

Practically? Wheels break off as the conveyer belt accelerates to improbable speed as the plane starts to accelerate forward under force of engines. Plane then goes up a little bit and then lands hard, conveyer belt slings it for a mile long skid backwards.

Uuuugggly.

I thought the first post was very clear that there is no mechanical failure...

As for practicality - we're talking about a mile long conveyor belt that can rotate at >100mph... this is pure hypotheticalness..